1. Field of the Invention
This invention relates to chain saws, and more particularly to a chain saw guide bar.
2. Description of the Prior Art
A chain saw consists of a motor, usually a small internal combustion engine, and an elongate protruding support member, known as a guide bar, around which the saw chain is driven. Some means must be provided to lubricate and cool the saw chain as it travels around the guide bar, and this is normally achieved by supplying oil to the chain as it leaves the motor housing. The chain moves in a direction such that it travels first along the upper part of the guide bar, and this creates a problem in carrying oil to the lower part of the guide bar, since by this time, even when the chain is initially flooded with oil, very little oil remains. The rest is dispersed into the atmosphere.
A further problem arises at the rounded tip of the guide bar. Normally sprockets are employed to guide the chain, and grease or oil must be applied via a small lubrication hole. If the sprocket bearings are not adequately lubricated, they will overheat and fail, generally without warning. With heavy use, the lubrication hole tends to become plugged with sawdust, and the user will often fail to apply the necessary lubricants, with disastrous consequences.
Since chain saws are generally intended to be hand operated, weight is also an important factor. A chain saw necessarily has to be operated with the bar cantilevered outward, and operator fatigue can be a serious problem. Weight can also be an important factor in some large mechanical saws. In the case of the most modern saws, designed to cut concrete and other relatively hard materials, the flow of coolant, normally water, is essential not only to cool the chain, but also to flush concrete, cement or other material from the chain to prevent excessive wear. This problem limits the viability of these modern tools.
Attempts have been made to address the above problems, and generally saw bars are made either in one piece with a guide groove for the chain machined into the bar, or in three pieces, with a center plate being recessed relative to the outer plates to provide the groove. The three parts are spot welded onto the bar.
In most prior art lubricating systems, attempts have been made to modify the chain groove to serve also as a circumferential oil channel. However, this arrangement suffers from the disadvantages outlined above. U.S. Pat. No. 3,578,779 is typical of such an arrangement.
U.S. Pat. No. 4,819,332 describes a chain saw guide bar with a through hole in the guide plate to which oil is supplied. Connection channels extend from the through hole to the chain saw guide grooves. While providing some improvement this arrangement does not significantly overcome the problems outlined above.